An image forming apparatus which uses an electrophotographic image forming method or an electrostatic recording method employs an endless belt as an image bearing member for bearing a toner image. For example, an image forming apparatus of the so-called intermediary transfer type employs an intermediary transfer belt, which is an endless belt onto which a toner image is transferred from two or more photosensitive members. Further, this type of image forming apparatus is provided with a belt cleaning apparatus for removing transfer residual toner (toner remaining on intermediary transfer belt after image transfer from belt) and other unnecessary residues (which also are referred to as residual toner, hereafter). A belt cleaning apparatus has a cleaning member for removing toner from the surface of the intermediary transfer belt; a container (casing) in which removed toner is stored and so on. The container is provided with a toner discharge opening, through which toner is discharged from the container and is sent to a storing apparatus (box for storing recovered toner).
Some belt cleaning apparatuses are structured so that they can be installed, as a part of a belt unit, into the main assembly of an image forming apparatus, or uninstalled, as a part of a belt unit, from the main assembly of an image forming apparatus. A belt unit is made up of an endless belt, and two or more rollers by which the endless belt is suspended and tensioned. Others may be structured so that they can be installed into, or uninstalled from, the main assembly of an image forming apparatus, without involving a belt unit.
If the toner discharge opening of the casing of the belt cleaning apparatus is left open when a belt cleaning apparatus is uninstalled, as an integral part of a belt unit, from the main assembly of an image forming apparatus, or uninstalled alone from the main assembly of an image forming apparatus, it sometimes occurs that toner scatters from the casing of the belt cleaning apparatus. In order to prevent the occurrence of this problem, some belt cleaning apparatuses are provided with a shutter for blocking the toner discharge opening of the casing. There is disclosed, in Japanese Laid-open Patent Application No. 2009-122345, a combination of an image forming apparatus and a cleaning apparatus therefor, structured so that, if the shutter member is open, a stopper prevents the belt cleaning apparatus from being uninstalled from the main assembly of the image forming apparatus.
This structural arrangement, however, requires an operator to open the shutter after the installation of a belt cleaning apparatus into the main assembly of an image forming apparatus, or to close the shutter before uninstalling the belt cleaning apparatus. Thus, this structural arrangement complicates the operation for installing, or uninstalling, the belt cleaning apparatus.
It is possible to structure a combination of an image forming apparatus and belt cleaning apparatus therefor so that as the belt cleaning apparatus is installed into, or uninstalled from, the main assembly of the image forming apparatus, the shutter is opened, or closed, respectively, by the movement of the belt cleaning apparatus. For example, it is possible to structure the combination so that when the belt cleaning apparatus is outside the main assembly of the image forming apparatus, the shutter is kept pressed in the blocking direction by a spring or the like, whereas as the belt cleaning apparatus is installed into the main assembly, the shutter comes under such force that is directed to open the shutter, and therefore, is kept open.
However, it has become evident that if a combination of an image forming apparatus and belt cleaning apparatus therefor is structured as described, the following problem arises. That is, as the belt cleaning apparatus is inserted into the main assembly of the image forming apparatus, the shutter is moved in the direction to unblock the toner discharge opening. Thereafter, the shutter remains under the force generated in the direction to press the shutter in the direction to block the toner discharge opening. This force affects the rotational movement of an intermediary transfer belt, in some cases. For example, it is possible that this force will affect the belt supporting-tensioning rollers and frame, by which the belt cleaning apparatus is supported, in their positional accuracy (whether or not they are parallel to each other). In particular, in a case where a belt cleaning apparatus is provided with a cleaning member, and is structured so that the cleaning member is pressed against a tension roller for adjusting an intermediary transfer roller in tension, with the presence of the intermediary transfer belt between the cleaning member and tension roller, the tension roller is sometimes changed in position by the force described above. If the tension roller is changed in position, the intermediary transfer belt is changed in tension. That is, the intermediary transfer belt is not provided with a preset amount of tension. Thus, it cannot be assured that the intermediary transfer belt rotates at a preset speed. Further, in a case where a belt unit is structured so that a tension roller doubles as a steering roller which automatically controls the belt deviation in terms of position, with the utilization of the balance in friction between the lengthwise end portions of the belt, the force described above becomes a large amount of load upon the steering operation of the tension roller, causing sometimes the tension roller to fail to properly steer the belt.
The earnest studies made by the inventors of the present invention regarding the issues discussed above revealed that structuring a combination of an image forming apparatus and belt cleaning apparatus therefor so that even when the belt cleaning apparatus is out of the main assembly of the image forming apparatus, the shutter can be held in a position in which it keeps the toner discharge opening unblocked, or a position in which it keeps the toner discharge opening blocked, and also, so that the shutter is opened or closed by the movement of the belt cleaning apparatus, which occurs as the belt cleaning apparatus is installed into, or uninstalled from, the main assembly of the image forming apparatus. This structural arrangement has its own issue. That is, if the shutter is already in its closed position for some reason or another when the belt cleaning apparatus is inserted into the main assembly of an image forming apparatus, it becomes sometimes impossible to insert the belt cleaning apparatus into the normal installation completion position. Moreover, it sometimes occurs that while the belt cleaning apparatus is inserted into the main assembly, toner falls out of the casing through the toner discharge opening, and contaminates the interior of the main assembly.